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1
Content available Freeze-proof durability of concrete incorporating recycled coarse aggregate
100%
Deng X. , Xue L. , Wang R. , Gao X.
Archives of Civil Engineering
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2019
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tom Vol. 65, nr 4
63--80
EN
The recycle of the building and demolition waste could reduce project expenses and save natural resources as well as solve problem about environmental risks incurred during the disposal of building waste. In this study, waste C30 concrete is taken an experimental material. The mass loss, ultrasonic velocity, dynamic modulus of elasticity and cubic compressive strength of recycled coarse aggregate concrete whose coarse aggregate replacement percentage is 25%, 50%, 75%, and 100% are tested and compared with NAC when the cycles of freezing and thawing are 0, 25, 50, 75, 100, 125, 150, 175, and 200 times. The results show: (1) Generally, the loss of mass, ultrasonic velocity, dynamic modulus of elasticity and cubic compressive strength constantly increase with the growth of freezing and thawing cycles. (2) Compared with the recycled concrete of other replacement percentages, the RAC50 shows relatively close performance to NAC in mass loss, the change of dynamic modulus of elasticity and cubic compressive strength. (3) Performances of RAC25 specimens are better than the other RAC specimens for the ultrasonic wave velocity.
2
Content available Investigating freeze-proof durability of air-entrained C30 recycled coarse aggregate concrete
100%
Deng X. , Liu Y. , Wang R.
Archives of Civil Engineering
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2021
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tom Vol. 67, nr 2
507--524
EN
Incorporation of air-entraining agent has improved recycled concrete freeze-proof durability. However, it is very lacking to study the role of the entraining agent. In this paper, the influence of an air-entraining agent on freeze-proof durability for the ordinary C30 recycled coarse aggregate (RCA) concrete and air-entrained C30 RCA concrete was investigated with the laboratory comparative tests. The mass loss, the dynamic modulus of elasticity, ultrasonic wave velocity and cubic compressive strength were measured during freeze-thaw cycles. The test result showed the concrete’s performance was similar to the ordinary concrete and was better than that of other recycled concretes when the content of RCA was 50% and 0.03% of air-entraining agent was added for C30 RCA concrete. Meanwhile, the addition of air-entraining agent has an improved effect on the performance of recycled concrete, but the effect was limited.
3
Content available remote Complete f-moment convergence of moving average process and its application to nonparametric regression models
100%
Yao C. , Wang R. , Chen L. , Wang X.
Probability and Mathematical Statistics
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2021
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tom Vol. 41, Fasc. 2
373--395
EN
In this paper, we establish a general result on complete f-moment convergence of the moving average process based on widely orthant dependent random variables, which generalizes some results in the literature. In addition, an application of complete consistency to nonparametric regression models is provided. Finally, we provide a numerical simulation to verify the validity of our theoretical results.
4
Content available Risk assessment of tunnel portals in the construction stage based on fuzzy analytic hierarchy process
100%
Deng X. , Wang R. , Xu T.
Archives of Civil Engineering
|
2018
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tom Vol. 64, nr 4/I
69--87
EN
This study presents a fuzzy analytic hierarchy process (FAHP) by integrating analytic hierarchy process (AHP) and fuzzy cognition to evaluate the construction risks of tunnel portals. Wuguanyi Tunnel is taken as the research objective to validate the performance of the proposed method. The result shows that the proposed decision making method can effectively identify risk factors and determine the risk level during the construction of tunnel portals. Finally, the corresponding control measures during the construction of the Wuguanyi Tunnel portal are proposed according to the risk assessment results.
5
Content available remote Efcient mixed domain pure P wave equations for 2D and 3D tilted transversely isotropic media
88%
Li B. , Wang D. , Zhou J. , Zhang Q. , Wang R.
Acta Geophysica
|
2020
|
tom Vol. 68, no. 3
605--618
EN
In transversely isotropic (TI) media, accurate and efcient pure P-wave extrapolation is the basis of seismic imaging and inversion algorithms. For pure P-wave equations in TI media, combining the fnite-diference (FD) method with the pseudospectral (PS) method is an efective solution. However, if the mixed-domain pure P-wave equation contains multiple wavenumbers, using the hybrid approach will involve multiple Fourier transforms, which will result in high computational costs. Referring to the weak anisotropy approximation, we propose a new approximate P-wave phase velocity expression. We then use an optimization strategy to reduce the number of wavenumber terms in the corresponding dispersion relations and derive the mixed-domain pure P-wave equations in 2D and 3D tilted transversely isotropic (TTI) media. Through numerical experiments in 2D and 3D TTI models, we verify the feasibility and efciency of the proposed mixed-domain P-wave equations.
6
Content available Acidic Corrosion Behaviour of Niobium-Added Welding Overlays Fabricated by Self-Shielded Metal-Cored Wires
75%
Liu D. , Wu Y. , Long W. , Wei P. , Wang R. , Zhou W.
Archives of Metallurgy and Materials
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2023
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tom Vol. 68, iss. 3
887--894
EN
Both corrosion and abrasion remove materials from some engineering components such as impact coal crusher hammers, pulverizer rings, chute liner, and rolls or molds. Intensive research has been done on improving the wear resistance of high chromium alloys, however, studies into corrosion resistance of high chromium alloys are insufficient. In order to determine the amount of ferroniobium addition in the wire to achieve the best corrosion resistance, and find out the mechanism of ferroniobium enhancing the corrosion resistance of the welding overlays, the high-Cr iron-based welding overlays with different niobium addition were fabricated by using self-made self-shielded metal-cored wires and their acidic corrosion resistance in 3.5 wt.% NaCl solution + 0.01 mol/L HCl solution were investigated by electrochemical corrosion test. The microstructure and corrosion morphology were characterized by OM, SEM, XRD and EDS. The polarization curves and values of Icorr, Ecorr and Rc indicate the corrosion resistance is at the highest with 3.6 wt.% niobium addition, and at the lowest when the niobium addition is 10.8 wt.%. The corrosion of welding overlay occurs in the matrix of microstructure. With the increase of niobium addition from 3.6 wt.% to 10.8 wt.%, the proportion of network eutectic structure in the welding overlay is increased. Up to 10.8 wt.%, the microstructure is transformed from hypereutectic structure into eutectic one, leading to a higher acceleration of corrosion rate. When niobium addition reaches 14.4 wt.%, the welding overlay is transformed into a hypoeutectic structure. The addition of niobium element consumes carbon element in the alloy, which makes the increase of chromium content in the final solidified matrix, leading to an improvement in corrosion resistance.
7
Content available remote An efficient low-frequency artifact suppression method at excitation time for excitation amplitude imaging condition
75%
Wang R. , Wang D. , Hu B. , Zhang W. , Zhou J. , Li B.
|
2023
|
tom Vol. 71, no. 3
1225--1240
EN
The excitation amplitude imaging condition (EAIC) is a high-resolution, computationally efficient, and low-storage imaging condition in reverse time migration (RTM). However, when there are strong reflection interfaces in the velocity model, they will produce low-frequency artifacts, which seriously contaminate the RTM image. The artifacts can be removed by the wavefield decomposition algorithm, but this process always performed by analytic time wavefield extrapolation, which needs extra wavefield extrapolation. Furthermore, an extra source wavefield extrapolation is required to determine the excitation time before the migration. Thus, the additional wavefield extrapolations can seriously damage the computationally efficient advantage of the EAIC. By taking advantage of the directivity and low storage of excitation amplitude, we present a low-frequency artifact suppression method with no extra wavefield extrapolation. Poynting vector, reference traveltime and minimum amplitude threshold are combined to constraint the excitation amplitude updating process, and it makes the excitation amplitude more consistent with the definition of excitation criterion. We can directly obtain a noise-free excitation amplitude without the source wavefield decomposition. Instead of the analytic time wavefield extrapolation, the time-bin technique and the windowed Hilbert transform are combined to achieve the receiver wavefield decomposition only at the excitation time. The numerical results show that our method can effectively suppress the low-frequency artifacts in the image with no extra wavefield extrapolation.
8
Content available Parameter identification of PMSM based on dung beetle optimization algorithm
75%
Yang X. , Cui Y. , Jia L. , Sun Z. , Zhang P. , Zhao J. , Wang R.
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2023
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tom Vol. 72, nr 4
1055--1072
EN
In this paper, a creative dung beetle optimization (CDBO) algorithm is proposed and applied to the offline parameter identification of permanent magnet synchronous motors. First, in order to uniformly initialize the population state and increase the population diversity, a strategy to improve the initialization of the dung beetle population using Singer chaotic mapping is proposed to improve the global search performance; second, in order to improve the local search performance and enhance the convergence accuracy of the algorithm, a new dung beetle position update strategy is designed to increase the spatial search range of the algorithm. Simulation results show that the proposed optimization algorithm can quickly and accurately identify parameters such as resistance, inductance, and magnetic chain of the PMSM, with significant improvements in convergence algebra, identification accuracy and stability.
9
Content available remote Research on the influence of external search strategy on enterprise innovation
75%
Li Z. , Zhang K. , Dang J. , Zheng S. , Wang R. , Wang Z.
Ecological Chemistry and Engineering. S
|
2023
|
tom Vol. 30, nr 1
111--116
EN
Based on the matching perspective, an analytical framework including external search strategy, organisational improvisation and structural flexibility is established. The purpose of this study is to explore the influence of external search strategy on firm innovation. The results show that, first, market information search has a positive impact on innovation quality and innovation speed. Secondly, the influence of technical knowledge search on innovation quality is moderated by organisational improvisation and structural flexibility. Thirdly, technical knowledge search has a positive impact on the innovation quality of enterprises. Fourthly, technical knowledge search has a positive impact on the innovation speed of enterprises.
10
Content available Optimization sealing and cooling to control gas intrusion in a floating-wall combustion chamber
75%
Shi H. , Wang R. , Chen M. , Wang J. , Yuan J. , Zhang Q. , Yang K.
|
|
tom Vol. 72, nr 2
art. no. e148834
EN
In response to the problems of high-temperature gas intrusion and ablation in the expansion slit between ceramic tiles under complex flow conditions in the floating-wall combustion chamber, as well as the issue of hooks exceeding their service temperature, numerical simulations and analysis were conducted for this paper. The study revealed the mechanisms of gas intrusion and sealing and proposed two evaluation metrics for evaluating the cooling effect: the maximum temperature of the hook and the proportion of high-temperature area on the sidewall of the tile. Furthermore, the CRITIC weighting method was used to analyze the weight of these metrics. Based on this, the spacing, radius, and length effects on sealing and cooling effectiveness were studied, and multi-parameter calculations and optimization were performed. The results showed that the degree of gas intrusion in the transverse slit was significantly higher than that in the longitudinal slit. In addition, the sealing method of the jet impingement could effectively cool the downstream of both the transverse and longitudinal slit. The spacing of the jet impingement holes had the greatest impact on the cooling effect, followed by the radius and length. Finally, when the spacing of the holes is 10 mm, the length is 18.125 mm, and the radius is 1.6 mm, the cooling effect is optimal, with the proportion of high-temperature area on the side wall of the tile being 20.86% and the highest temperature of the hook reaching 836.02 K.
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