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Impact of climate warming on the surface water temperature of plateau lake

Peng Zongqi, Yang Jiaying, Luo Yi, Yang Kun, Shang Chunxue

Acta Geophysica

2021

Vol. 69, no. 3

895--907

Lake surface water temperature (LSWT) is a vital indicator in evaluating the ecological environment and has a direct or indirect impact on regulating physical, chemical, and ecological processes of lakes. Changes in LSWT have a huge impact on the water quality, ecosystem function, and biome composition of the entire lake. In this study, we selected Dianchi Lake as the research area, the monthly average LSWT data collected at the monitoring station from 1998 to 2009 were used as the calibration dataset. The error analysis dataset is the average annual temperatures of the Dianchi Lake extracted from MODIS remote sensing images from 2001 to 2017. The daily average LSWT of Dianchi Lake was estimated by the air–water model and the historical changes from 1980 to 2017 of the LSWT were reproduced. The research draws a conclusion that the LSWT of Dianchi Lake has been greatly afected by air temperature over the past 37 years. LSWT and the annual average air temperature correlation coefcient were R>0.9. Both the air temperature and LSWT assumed an increasing tendency. The annual average LSWT increased with the rate of 0.36 °C/decade, and the annual average warming rate of the air temperature was 0.47 °C/decade. The monthly average LSWT and air temperature showed a signifcant correlation at a confdence interval of α=0.001. The LSWT of Dianchi Lake increased signifcantly in February, March, and December. The periodicity of the seasonal mean air temperature change was consistent with that of the LSWT in Dianchi Lake. The relative lag of the thermal response of the LSWT to climate warming was also observed. This study flls in the gaps in the long-term sequence data on the LSWT of Dianchi Lake and reveals the efect of climate warming on the LSWT of low-latitude plateau lakes.

Assessing surface fatigue crack growth in railway wheelset axle

Rudavskyi D. V., Kaniuk Yu. I., Duriagina Z. A., Kulyk V. V., Shefer M. S., Dolinska I. Ya.

Archives of Materials Science and Engineering

2020

Vol. 106, nr 2

59--67

Purpose: The aim of the proposed research is to create a calculation model of surface fatigue crack growth at the axle of railway wheelset working under operational loads. Design/methodology/approach: The energy approach of the fracture mechanics was used to formulate the calculation model of fatigue crack propagation at the wheelset axle surface. The method of least squares was used to determine the investigated material mechanical constants that the kinetic equations of the calculation model contain. The system of differential equations of crack growth kinetics was solved numerically using the Runge-Kutta method. Findings: On the basis of the energy approach of the fracture mechanics the calculation model of fatigue macrocrack growth in three-dimensional elastic-plastic body in case of a mixed-mode I+II+III macromechanism of fracture has been built. On the basis of the created calculation model, the kinetics of the growth of fatigue cracks was investigated both in the middle part of the wheelset axle and in the axle journal. Research limitations/implications: The results obtained on laboratory specimens should be tested during a real railway wheelset axle investigation. Practical implications: The created calculation model can be used in practice to formulate method of residual lifetime estimation of railway wheelset axle. Originality/value: It was shown, that surface crack kinetics depends not only on the crack initial area but also significantly depends on the crack edge geometry and comparatively small crack-like defects at the wheelset axle surface can reach critical sizes in comparatively short run. It has been found that mechanical shear stresses caused by the weight of the loaded railway wagon in the cross section of the wheelset axle journal can significantly accelerate the growth of the transverse fatigue crack at the axle surface, reducing the period of crack subcritical growth by about 20%.

Strains and self-stresses estimation in the expansive concrete members reinforced with GFRP bars

Tur V., Semianiuk V.

Inżynieria Bezpieczeństwa Obiektów Antropogenicznych

2016

Nr 4

3--9

Advantages of the self-stressed concrete members with FRP reinforcement are described. Analytical model for the restrained expansion strains (self-stresses) estimation in the self-stressed concrete members reinforced with FRP bars is proposed. Established modified strains development model (MSDM) is based on deformation compatibility approach in combination with taking into account imposed internal force in reinforcement as an additional restriction for the expansion strains development. Comparison of experimentally established and predicted data that was obtained in accordance with the proposed model for the case of GFRP bars uniaxially symmetrically reinforced high expansion energy capacity concrete members is presented. Verification of the proposed MSDM has shown a good agreement between calculated and experimental values that indicates its validity for the design of the self-stressed concrete members with GFRP reinforcement.